The mixed acetal functionality exists in a variety of biologically important molecules, and reactions targeting sulfur are important in such systems. Hence studies of the mechanisms of such reactions have been carried out over the past several decades, with mixed success. Our previous investigations of the mechanisms of hydrolysis of O,S-acetals promoted by metallocomplexes have defined the methodology used to study the kinetics of acyclic. O,S-acetals. The acyclic structural feature was important for these initial studies because it precluded the potential return of the sulfur moiety at the spectral concentrations at which the experiments were conducted. We now have established that for mercury halide complexes, (1) the metallocomplex is a reagent, not a catalyst, (2) the state of complexation of mercury(II) is critical in determining its reactivity, (3) the attenuation of the metallocomplex reactivity on replacing aquo ligands by halide are as predicted by the concepts of hard and soft acid/base theory (HSAB), and (4) there is little effect on reactivity effected upon changing the structure of the acyclic O,S-acetal. The proposed research has three major objectives: (i) examination of the source of the substantial difference in reactivity between acyclic and cyclic O,S-acetals, (ii) exploration of the relationship between the tow- electron process (e.g. the Lewis Acid behavior of mercuric complexes) and the one-electron process (e.g. redox behavior), and (iii) examination of the reactivity of the unique hemiacetal intermediates. This research affords an excellent opportunity for undergraduate and M.S. students to become involved in research. Past experience indicates that several students from ethic groups traditionally underrepresented in biomedical research careers would (i) be attracted to work on this research, (ii) present their work at professional conferences, (iii) be coauthors of publications in peer reviewed chemical journals and (iv) enter Ph.D. programs upon graduation.